Losing your hair sucks. I know first hand as I'm going through the same thing right now. Since the beginning of September my hair has been falling out in copious amounts...I'm losing over 500 hairs a day. It's really scary to run my hands through my hair and see so much come out. I've calculated that at this rate, I'll be bald within 6 months if it doesn't grow back.
I've done tons of research online and talked to a doctor. What I've learned is that most female hair loss can be attributed to Telogen Effluvium (here's a website that tells you all about it: Medscape: Medscape Access). It can be caused by numerous things: illness or other physiological stress, emotional stress, excesses or deficiencies in certain vitamins and minerals, medications, hyper or hypoactive thyroid, and anemia, just to name a few. Telogen Effluvium (TE) often resolves spontaneously within 6 months, but some report it lasting years, in that case it is called Chronic Telogen Effluvium. I've read that any insult to your body or hair is a result of something that happened three months previously to when you first started noticing hair fall out. Did you start or stop taking a new medication (many report stopping birth control can cause hair fall out), change your diet, begin taking a new supplement, or have any chemical service performed on your hair? Also, it is important to remember that it is normal to lose anywhere from 50-100 or so hairs a day and that we often shed more in the fall than any other time of the year.
From what I've read there is no treatment for TE. You simply have to wait until it stops. I perform a weekly count to just to evaluate whether or not the hair loss is slowing down but it can make you crazy and stress can just exacerbate the problem. The best thing you can do is to go to a dermatologist and have some basic blood tests run and check your thyroid and iron levels. If you can remove whatever is the culprit or treat the deficiency, your hair will begin to recover, but it will take time...likely months.